Electric vehicles, for example, are equipped with a vehicle proximity warning device, which alerts pedestrians to their approach. A typical vehicle proximity warning device is installed in high-temperature, severe environments such as in the engine compartment exposed to oil or rain splash during driving. The engine compartment is mounted with a motor as the power source of the electric vehicle. The vehicle proximity warning device includes a loudspeaker, a loudspeaker box in which the loudspeaker is accommodated, and an electronic circuit for driving the loudspeaker.
As shown in FIG. 12, according to Patent Literature 1, loudspeaker box 21 includes box 22 with opening 23, and lid 24 for covering opening 23. Loudspeaker box 21 accommodates loudspeaker 25.
Loudspeaker box 21 is installed in a position exposed to rain splash from the road surface while the electric vehicle is driving. Therefore, lid 24 is desired to protect loudspeaker 25 and to allow the alarm from loudspeaker 25 to be clearly emitted. To meet these purposes, lid 24 includes louver 26, which covers opening 23.
Patent Literature 2 discloses an attachment to a loudspeaker. This attachment is installed not in adverse environments exposed to rain water like vehicle proximity warning devices but in a car instrument panel. The attachment includes reinforcing ribs on the back of the loudspeaker grille in order to reinforce the rigidity of the grille having many small holes as sound holes. To be more specific, the disclosed reinforcing ribs are zigzagged or hexagonal. These ribs prevent the grille from being dented when accidentally pressed. However, the spacing between the ribs or the size of the hexagonal holes are too large as the sound holes of the loudspeaker grille. Thus, the ribs alone cannot protect the loudspeaker.
Furthermore, as described above, the vehicle proximity warning devices are installed in severe environments, so that widely used diaphragms are made from resin or resin fiber.
Meanwhile, Patent Literature 3 discloses a loudspeaker diaphragm with a two- or three-layer cross-sectional structure, which improves the sound quality of the loudspeaker. In patent Literature 3, the paper liquids used in the first and second paper-making processes contain pulp, and the paper liquid used in the third process contains Manila hemp.